The nose landing gear on Boeing 737 jets like the Southwest Airlines plane that malfunctioned Monday at LaGuardia Airport has collapsed or failed to retract in at least 20 incidents worldwide since 1990, according to data from the National Transportation Safety Board.
At least three of the malfunctioning nose gear have occurred since 2007 on Southwest Airlines jets, according to the NTSB and media reports at the time.
Nose gear troubles are usually caused by technical malfunctions or human error.
Aviation experts cautioned against drawing any firm conclusion from the NTSB statistics: The Boeing 737 model aircraft is reliable, said John Goglia, an aviation consultant and former member of the NTSB.
"They've had their share" of incidents, Goglia said of the Boeing jet. "But there are a lot of those planes."
The NTSB is investigating the hard landing of the Southwest Airlines 737-700 at LaGuardia.
"The twin-engine jet's nose landing gear collapsed rearward and upward into the fuselage, damaging the electronics bay, which houses avionics and other equipment," the NTSB said in a statement. "The exterior of the airplane was also damaged from sliding 2,175 feet on its nose along Runway 4 before coming to rest, off to the right side of the runway."
Neither the NTSB or Boeing would comment on what caused the nose gear to collapse.
A Boeing statement said the company has "people on the ground supporting our customer and is providing technical assistance to the NTSB."
Several passengers reported hearing a loud bang echo through the cabin of Flight 345 before it filled with smoke after the jet pitched forward. Nine passengers were injured, none seriously, the NTSB said Tuesday. The 145 passengers and five crew used an inflatable emergency slide to exit the plane after it screeched to a halt on a patch of grass just off the tarmac.
Southwest Airlines said the aircraft has been in service since October 1999 and was last inspected July 18.
The same type of nose gear that collapsed on the Southwest Airlines jet Monday is equipped on 737 jets used by other airlines.
Southwest had a similar equipment failure during a 2012 landing in El Paso, Texas, and two jets from the Southwest 737 fleet had nose gear malfunctions in 2007, according to news reports.
In the 2012 malfunction, part of the nose gear mechanism on a flight landing in El Paso "experienced a structural failure," according to NTSB documents.
In 2007, two Southwest flights were affected by nose gear malfunctions in California. In June of that year, Flight 3050 en route to San Diego was diverted to Oakland International Airport after its nose gear system failed and then collapsed upon landing. In September, the pilot of Southwest Airlines Flight 614 had to turn around shortly after departing because the 737's nose gear wouldn't retract, according to news reports at the time.
Since 2004, the Federal Aviation Administration has issued at least two Airworthiness Directives relating to the entire landing gear of the Boeing 737.
One directive ordered repairs to landing gear warning systems because a malfunction "could jeopardize a safe flight and landing." Another directive required Boeing maintenance crews to lubricate mechanisms to prevent cracking that could lead to a collapse of the main landing gear.
After more than six nose gear collapses between 2004 and 2006 resulting from towing and pushbacks, Boeing issued a service letter to maintenance personnel about proper technique to reduce stress on nose gear, according to NTSB records.
The 737's landing gear doesn't require more maintenance or have more failures than other commercial jet models, said aircraft maintenance mechanic Edward Libassi, president of A&P Aircraft Maintenance based at Long Island MacArthur Airport.
"I know Southwest does follow all the perimeters of their work scope," said Libassi, who works on more than 600 planes, including Southwest's fleet, each year at MacArthur. "You can't fly that many airplanes out of that many bases without something happening."